The present invention relates to a keypad of a terminal such as a cellular phone, the handset or base of a wired or wireless telephone, or an electronic organizer, and more particularly to a keypad backlighting device.
In general, portable or handheld terminals are provided with a keypad as an input device for inputting information, searching stored information and multimedia files for execution, and selecting menus. Although a touch screen may be used as the input device while also acting as a display device, it is the keypad, composed of an array of a number of keys, which is typically used for input, search, and execution functions. The keypad is provided with a backlighting device to enable users to easily recognize and operate it even in the dark.
FIG. 1 is a sectional view showing the construction of a keypad provided with a backlighting device according to the prior art. As shown in FIG. 1, the keypad 100 includes a PCB 101 having dome switches 111 arranged on a surface thereof and a silicon pad 102 having a number of key tops 123 arranged thereon. The PCB 101 may be a flexible PCB, if necessary.
The key tops 123 are positioned in such a manner that they correspond to the respective dome switches 111. The silicon pad 102 has contact protrusions 121 formed thereon while facing the corresponding dome switches 111. When the user operates the key tops 123, the silicon pad 102 deforms accordingly. As a result, the contact protrusions 121 press and actuate the corresponding dome switches 111. The key tops 123 have characters printed thereon, which correspond to key values assigned thereto, respectively, so that the user can recognize the characters and functions assigned to the key tops 123 and operate them as desired.
The keypad is provided with a lighting device, which uses a light source 113 (e.g. LED), so that it can be used conveniently even in the dark. According to the user's setting, the lighting device lights the keypad either every time it is used or only at night.
The light sources 113 composing the lighting device are positioned on the PCB 101 and below both sides of the respective key tops 123. Light generated by the light sources 113 diffuses through the silicon pad 102 and lights the characters printed on the key tops 123.
However, light sources 113 of conventional lighting devices, constructed as above, are monochrome emitters and light the keypad 100 in a uniform manner. The number of light sources required consequently equals or exceeds the number of keys constituting the keypad. This complicates the assembly process and increases the cost of manufacturing. In particular, the installation a large number of LEDs on the PCB inevitably complicates the printed circuit pattern and entails an additional installation process. This increases the manufacturing cost. Moreover, any difference in luminance among the light sources makes the overall lighting of the keypad uneven.
In order to satisfy the users' various tastes and demands regarding portable terminals, manufacturers are trying to diversify not only the design and function of terminals, but also the color of light used for illuminating the keypad. Using conventional monochrome emitters as light sources in order to realize various colors, however, requires the additional installing of light sources for generating different colors. Alternatively, a single package may provide a number of emission chips for generating different colors. In either case, it is difficult to realize desired colors, because of luminance differences in the light generated by respective light sources and the resulting difference in color, to say nothing of increased manufacturing cost.
Generating white light requires the mixing of red, green, and blue lights. However, variation in characteristics of elements used in the manufacturing process, i.e., light sources or emission chips for generating different colors, makes it difficult to realize brilliant white light.